Headphone with cross feeding ambience control

ABSTRACT

A stereophonic headphone includes ambience control potentiometers connected in series with each audio transducer. A portion of the audio signal applied directly to each audio transducer is coupled to the ambience control potentiometer of the other audio transducer and is applied to the other audio transducer 180* out of phase. A mixing of the left and right audio channels is thus obtained and can be controlled by the listener to provide the desired binaural listening effect.

United States Patent 1191 Turner et al.

[ Dec.2, 1975 1 1 HEADPHONE WITH CROSS FEEDING AMBIENCE CONTROL [75]Inventors: Jacob C. Turner; Douglas M. Elliott,

both of Milwaukee, Wis.

[73] Assignee: Koss Corporation, Milwaukee, Wis.

[22] Filed: July 10, 1974 21] Appl. No.: 487,031

[52] US. Cl. 179/1 GP; 179/156 R; 179/1 G [51] Int. Cl. H04R 5/02 [58]Field of Search 179/1 GP, 156 R, 1 G, 182,

3,329,772 7/1967 Farrell 179/1 G OTHER PUBLICATIONS Journal of the AudioEngineering Society, B. B. Bauer, Apr. 1961, Vol. 9. N0. 2, pp. 148-151.

Primary Examiner-Kathleen H. C'laffy Assistant Examiner-Tommy P. ChinAttorney, Agent, or FirmQuarles & Brady [57] ABSTRACT A stereophonicheadphone includes ambience control potentiometers connected in serieswith each audio transducer. A portion of the audio signal applieddirectly to each audio transducer is coupled to the ambience controlpotentiometer of the other audio transducer and is applied to the otheraudio transducer 180 out of phase. A mixing of the left and right audiochannels is thus obtained and can be controlled by the listener toprovide the desired binaural listening effect.

3 Claims, 3 Drawing Figures Patent Dec. 2, 1975 Sheet 1 of 2 US. PatentDec. 2, 1975 Sheet 2 of2 3,924,072

HEADPHONE WITH CROSS FEEDING AMBIENCE CONTROL Background of theInvention The field of the invention is headphones, and particularly,high fidelity headphones for reproducing stereo phonically recordedprograms.

Commercially available stereophonically recorded program materialsinclude two completely separate channels of program information whichare formed, for example, by combining recorded signals from microphonesdisposed at many locations in the recording studio. When reproduced by apair of loudspeakers located in a room, such stereophonic programmaterial provides not only directionality, but also, because the soundfrom each loudspeaker reaches both ears of the listener, either directlyor after being reflected from surfaces in the room, the left and rightchannels are mixed before they reach the listeners ears to provide apanorama of sound.

The manner in which the sound from each loudspeaker mixes with that ofthe other before reaching the ear of the listener depends upon numerousfactors. For example, the position of the listener with respect to theloudspeakers, the frequency of the program material, and the size, shapeand contents of the room in which the loudspeakers and listeners arelocated all contribute to this mixing process. The mixing is not,therefore, merely the addition of a portion of one channel to the other,but instead, involves the complex addition of phase-shifted sounds. Asimilar mixing process occurs if the listener hears the program materiallive as it is being recorded, and it is this mixing process whichprovides true binaural listening.

A preponderance of commercially available stereophonically recordedprogram materials presume that some mixing of the left and rightchannels will occur when played back through loudspeakers. However, whenreproduced through headphones, this complex mixing of the left and rightchannels does not occur, and instead, the program material in the leftchannel is coupled directly to the left ear of the listener and theprogram material of the right channel is coupled directly to the rightear. Although the resulting complete separation of the left and rightchannels provides a most pleasing listening experience, a panorama ofsound is difficult to achieve with some recorded materials. For example,when listening to a vocalist accompanied by an orchestra, the vocalistmay appear in the center, the brass on the right and the strings on theleft. Rather than a continuous blending of these three apparent sourcesof sound, however, gaps may appear between them. The extent to whichthis effect is noticed varies greatly depending on the nature of theprogram material, the type of recording technique used, and thesensitivites of the individual listener.

Summary of the Invention The present invention relates to a stereophonicheadphone in which means are provided for introducing ambient programinformation into each ear of the listener which electrically simulatesthe mixing which occurs when listening to stereophonically recordedprograms through a loudspeaker system. More specifically, the inventionresides in a stereophonic headphone having a first audio transducerwhich connects to receive the audio signal from one channel of astereophonic re- LII cording, a second audio transducer connected toreceive an audio signal from the second channel of the stereophonicrecording, first means for coupling a portion of the audio signalapplied to the first audio transducer to the second audio transducer andimparting a substantial phase shift thereto, and second means forcoupling a portion of the audio signal applied to the second audiotransducer to the first audio transducer and imparting asubstantialphase shift thereto.

A general object of the invention is to simulate the mixing ofstereophonically recorded program material which occurs when reproducedthrough a loudspeaker system. This mixing is accomplished by sampling aportion of the audio signal applied to each transducer and coupling itto the other transducer. Rather than merely adding the sampled audiosignal to the other transducer, however, a substantial phase shift isfirst imparted to it. Therefore, rather than merely reducing theseparation, or stereophonic effect, the mixing of the two separatechannels fills in the gaps and provides a panorama of sound withoutdiminishing separation.

Another object of the invention is to provide a means for adjusting theamount of mixing of the two audio signals to enable the listener toblend the two channels to his own particular taste. This is accomplishedby ambience control potentiometers which are mounted to each cup of theheadphone and which are electrically connected to control the amount ofcoupling between channels.

A more specific object of the invention is to provide a headphone inwhich the user may alter the phase and mixing of the two audio channels.In addition to the ambience control potentiometers, a phase switchisprovided which allows the phase of one audio channel to be reversedwith respect to the other channel. Many additional blending effects canthus be obtained by the user merely by changing the phase switch.

The foregoing and other objects and advantages of the invention willappear from the following description. In the description reference ismade to the accompanying drawings which form a part hereof, and in whichthere is shown by way of illustration a preferred embodiment of theinvention. Such embodiment does not necessarily represent the full scopeof the invention and reference is made to the claims herein forinterpreting the breadth of the invention.

Brief Description of the Drawings FIG. 1 is an electrical schematicdiagram of the invented ambience headphone,

FIG. 2 is a front view with parts cut away of the invented ambienceheadphone, and

FIG. 3 is a sideview of one cup which forms a part of the headphone inFIG. 2.

Description of the Preferred Embodiment Referring particularly to FIG.2, the invention is embodied in a stereophonic headphone which'includesa head band 1 which extends over the listeners head and provides supportfor a left cup 2 and a right cup 3. Tte cups 2 and 3 are substantiallysimilar and each includes a liquid filled cushion 4 and 5 which providesa comfortable fit over the liste ners ears. An-audio transducer 6 ismounted in the cup 2 and is positioned to direct sound through a centralopening in the cushion 4 into one ear of the listener, and similarly, anaudio transducer 7 is mounted in the cup 3 to direct sound into thelisteners other ear. A cable 8 connects the left cup 2 with astereophonic signal source and a connecting cable 9 supported by thehead band 1 electrically couples the left cup 2 to the right cup 3.Structurally, the headphone is substantially similar to the model PRO/-4AA headphone which is commercially available from the Koss Corporation.

Referring particularly to FIG. 1, the cable 8 includes three leads: aground lead 10; a left channel lead 11; and a right channel lead 12. Theleft channel lead 11 connects to a positive terminal 13 on the leftaudio transducer 6 and connects through a first coupling resistor 14 toone movable contact of a double-poledouble-throw ambience switch 15. Theright channel lead 12 connects to the other movable contact on theambience switch 15 through a second coupling resistor 16 and it alsoconnects to one movable contact on a double-pole-double-throw phasereversal switch 17.

The ground lead 10 is electrically common to both the left and rightaudio channels. It connects to one pair of stationary contacts 18 on theambience switch 16 and it also connects to one end of the resistanceelement in a left ambience control potentiometer l9 and to one end ofthe resistance element in a right ambience control potentiometer 20. Theother end of the resistance element in the left ambience controlpotentiometer 19 connects to a negative terminal 21 on the left audiotransducer 6 and the other end of the resistance element in the rightambience control potentiometer connects to the other movable contact 22on the phase switch 17. A first pair of stationary contacts 24 on thephase switch 17 connect to a positive terminal 25 and a negativeterminal 26 on the right audio transducer 7, and they are crossconnected with a second set of stationary contacts 27 on the phasereversal switch 17.

The wiper on the left ambient control potentiometer 19 connects with astationary contact 28 on the ambience switch 15. When the ambienceswitch 15 is in its operating position, therefore, the wiper isconnected to the second coupling resistor 16, Similarly, the wiper onthe right ambience control potentiometer 20 connects with a stationarycontact 29 on the ambience switch 15, and when the ambience switch 15 isin its operating position, the wiper connects with the first couplingresistor 14. 1

The ambience switch 15 is operable between two positions and when it isswitched to its test position, the coupling resistors 14 and 16 are bothconnected to the ground lead 10 and the headphone operates in aconventional manner. More specifically, the left audio signal on thelead 11 is applied to the positive terminal 13 on the left audiotransducer 6 and is voltage divided between the audio transducer and theleft ambience control potentiometer 19. Similarly, the right audiosignal is applied through the lead 12 and phase switch 17 to the rightaudio transducer 7. It is voltage divided between the audio transducer 7and the right ambience control potentiometer 20. In this standard modeof operation left channel program information is applied to the leftaudio transducer 6 and right channel program information is applied tothe right audio transducer 7. No mixing is provided, however, the phaseof the right channel audio signal can be reversed 180 by operating thephase switch 17.

When the ambience switch 15 is in its operating position, the left andright audio channels are mixed by coupling a portion of the left channelsignal to the right audio transducer 7 and coupling a portion of theright channel signal to the left audio transducer 6. More specifically,the left channel signal on the lead 11 is applied through the firstcoupling resistor 14 to the right ambience control potentiometer 20 andthe right channel signal on the lead 12 is applied through the secondcoupling resistor 16 to the left ambience control potentiometer 19. Themixing which is thus obtained is not merely the addition of a portion ofthe right channel to the left and vice versa, but instead, involves asubstantial phase shift of the cross coupled audio signals. The leftchannel signal is coupled to the right transducer 7 through the seriesconnected right ambience control 20 and is applied 180 out of phase withrespect to the applied right channel signal. Similarly, the rightchannel signal is coupled to the left audio transducer 6 through theseries connected left ambience control potentiometer 19 and is applied180 out of phase with respect to the applied left channel signal. Theamount of mixing which occurs is controlled separately for each channelby the position of the wipers on the ambience control potentiometers 19and 20.

Referring particularly to FIGS. 2 and 3, the ambience controlpotentiometers are physically mounted in the respective headphone cups 2and 3 where they are easily accessible to the listener. The amount ofmixing of the stereophonically recorded program can thus be separatelycontrolled by the listener to obtain the most pleasing effect. The phaseswitch 17 is also mounted to the right cup 3 to add yet another easilyaccessible control for the listener.

Although the values of the coupling resistors 14 and 16 and the valuesof the ambience control potentiometers 19 and 20 can be variedconsiderably, there are a number of design constraints which lead to theparticular values used in the preferred embodiment described herein. Theresistance of each audio transducer 6 and 7, for example, isapproximately 220 ohms and to insure efficient operation of theheadphones, the resistance of the series connected ambience controlpotentiometers 19 and 20 must be limited to a reasonable value. On theother hand, commercially available audio amplifiers to which theheadphones are attached, typically include a series resistor of from to600 ohms in each of the leads 11 and 12. It has been discovered thatunless the resistances of the ambience control potentiometers l9 and 20are significant with respect to these series connected resistors, thecontrol of the mixing is somewhat unpredictable and noticeablynonlinear. A value of 1,000 ohms was selected for each ambience controlpotentiometer 19 and 20 and is believed to be a reasonable compromisebetween these two design objectives.

The values of the coupling resistors 14 and 16 are determined primarilyby the amount of maximum mixing that is desired. Just as the amount ofmixing is very subjective, so is the maximum amount, and therefore, thevalues of the coupling resistors 14 and 16 can be varied considerablyaccording to taste. A value of 390 ohms has been chosen for the couplingresistors 14 and 16 in the preferred embodiment described herein andthis value provides a most pleasing effect.

A stereophonic headphone has been described which provides the listenerwith a means of introducing and controlling the ambient sounds whichreach his ears. These ambient sounds simulate the mixing of sounds whichoccurs when listening to sterephonic program material binaurally.

We claim:

1. In a stereophonic headphone having a first audio transducer mountedin a first cup for positioning over one ear of a listener and having apair of input terminals, a second audio transducer mounted in a secondcup for positioning over the other ear of the listener and having a pairof input terminals, and cable means for coupling separate audio signalsto each of said audio transducers, the improvement therein comprising:

a left channel lead in said cable means connected to one input terminalon said first audio transducer;

a right channel lead in said cable means connected to one input terminalon said second audio transducer;

first ambience resistor means mounted in one of said cups and connectedbetween the other terminal on said first audio transducer and a groundlead in said cable means, said first ambience resistor means beingoperable to voltage divide an audio signal applied across said leftchannel lead and said ground lead with said first audio transducer;

a first coupling resistor mounted within one of said cups and connectedto the right channel lead and coupled to said first ambience resistormeans, said first coupling resistor being operable to couple a portionof said left channel signal generated across said first ambienceresistor means to said one input terminal on said second audiotransducer;

a second ambience resistor means mounted within one of said cups andconnected between the other terminal on said second audio transducer andsaid ground lead, said second ambience resistor means being operable tovoltage divide an audio signal applied across said right channel leadand said ground lead with said second audio transducer; and

a second coupling resistor mounted within one of said cups and connectedto the left channel lead and coupled to said second ambience resistormeans, said second coupling resistor being operable to couple a portionof said right channel signal generated across said second ambienceresistor means to said one input terminal on said first audiotransducer.

2. The stereophonic headphone as recited in claim 1 which includes adouble pole single throw ambience switch mounted within one of said cupsand having one pole connected in series circuit with said first couplingresistor and its other pole connected in series circuit with said secondcoupling resistor.

3. The stereophonic headphone as recited in claim 1 in which said firstand second ambience resistor means are potentiometers, each having aresistance element and a slider.

1. In a stereophonic headphone having a first audio transducer mountedin a first cup for positioning over one ear of a listener and having apair of input terminals, a second audio transducer mounted in a secondcup for positioning over the other ear of the listener and having a pairof input terminals, and cable means for coupling separate audio signalsto each of said audio transducers, the improvement therein comprising: aleft channel lead in said cable means connected to one input terminal onsaid first audio transducer; a right channel lead in said cable meansconnected to one input terminal on said second audio transducer; firstambience resistor means mounted in one of said cups and connectedbetween the other terminal on said first audio transducer and a groundlead in said cable means, said first ambience resistor means beingoperable to voltage divide an audio signal applied across said leftchannel lead and said ground lead with said first Audio transducer; afirst coupling resistor mounted within one of said cups and connected tothe right channel lead and coupled to said first ambience resistormeans, said first coupling resistor being operable to couple a portionof said left channel signal generated across said first ambienceresistor means to said one input terminal on said second audiotransducer; a second ambience resistor means mounted within one of saidcups and connected between the other terminal on said second audiotransducer and said ground lead, said second ambience resistor meansbeing operable to voltage divide an audio signal applied across saidright channel lead and said ground lead with said second audiotransducer; and a second coupling resistor mounted within one of saidcups and connected to the left channel lead and coupled to said secondambience resistor means, said second coupling resistor being operable tocouple a portion of said right channel signal generated across saidsecond ambience resistor means to said one input terminal on said firstaudio transducer.
 2. The stereophonic headphone as recited in claim 1which includes a double pole single throw ambience switch mounted withinone of said cups and having one pole connected in series circuit withsaid first coupling resistor and its other pole connected in seriescircuit with said second coupling resistor.
 3. The stereophonicheadphone as recited in claim 1 in which said first and second ambienceresistor means are potentiometers, each having a resistance element anda slider.